The present invention relates to a process for the introduction of liquid feeds to a polymerisation process.
The production of polymer powder by polymerisation reactions of monomers in the presence of catalysts is well-known. For example, processes are known and widely operated commercially using both fluidised bed reactors and slurry phase reactors.
In a slurry polymerisation process, for example, the polymerisation is conducted in a stirred tank or, preferably, a continuous loop reactor in which a slurry of polymer particles in a liquid medium comprising hydrocarbon diluent is circulated. During the course of polymerisation, fresh polymer is generated by the catalytic polymerisation of monomer and polymer product is removed from the reactor by removing a portion of the slurry.
The slurry withdrawn may be treated to separate the polymer particles from the hydrocarbon diluent and other components, such as unreacted monomers, which it is generally desired are recycled to the process.
A polymerisation process generally includes feed systems for fresh monomer and comonomer, as well as for fresh inert liquids. Fresh feeds of monomer and co-monomer for example are fed to the polymerisation process to replace monomer and comonomer consumed in the reaction. Although inert liquids don't react they can be lost from the system in purges or as residual amounts in the polymer passed to downstream storage and processing.
Thus, it is common to have fresh feeds for each of the process components. The fresh feeds are usually treated to remove components which may act as poisons in the polymerisation process, or which, even if not poisons, may otherwise build-up in the process and require larger purges to be taken. (Unless separation of the component is very efficient, any increase in purge rates is likely to lead to increased loss of useful materials as well.)
U.S. Pat. No. 6,051,631, for example, discloses a process to treat fluid streams to remove undesirable compounds, in particular to treat monomer, comonomer and diluent streams to a polymerisation process.
In general, treatment comprises passing the respective streams to a treatment bed, usually comprising a fixed bed of a suitable absorbent for the impurities it is desired to remove. Two or more treatment beds for a particular feed may be provided in parallel to allow one to be regenerated whilst another is in use, as described in U.S. Pat. No. 6,051,631. It is also possible that certain streams, such as diluent and comonomer, can be mixed and passed to a common treatment bed, such as also described in U.S. Pat. No. 6,051,631.
The treated streams are then passed to the reactor (or reactors where more than one are present).